<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function getRandomColor(flag) {
            let arr = ['0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f']
            let str = '#'
            if(flag){
                for(let i = 0;i < 6; i++){
                    let ran = Math.floor(Math.random() * arr.length)
                    str += arr[ran]

                }
                return str
            }else {
                let r = Math.floor(Math.random() * 256)
                let g = Math.floor(Math.random() * 256)
                let b = Math.floor(Math.random() * 256)
                return `rgb(${r},${g},${b})`

            }

        }

        console.log(getRandomColor(true))
        console.log(getRandomColor(false))

        const div = document.querySelector('div')
        div.style.backgroundColor = getRandomColor(true)

    </script>
</body>
</html>